Diving Performance - Beyond Drag (article Series And Discussion)

[REVAN]

Then there are ones that are interested in helicopter turns and backing up. A lot of this is DIR based from the root since I never heard of any of this prior to DIR.

I would think that if a group of divers can convince a significant fraction of the diving population that they should be swimming backwards, then a different group of divers should be able to convince a more significant fraction of divers that they should be swimming forward with a reasonable level of efficiency. I think the latter makes more sense, so it should be an easier sell. 30 years ago there was no DIR. Someone had to make DIR diving a thing.

Ha, I'm probably not the first to think of this, but I just realized that DIR could stand for Diving In Reverse! Maybe I need a catchphrase, DFE (Diving Forward Efficiently). Who's got something better?

 

[John C. Ratliff]

DIR: "Doing It Right," or how about "Diving In Reverse." The Aqueon had the capability, with a hook, to reverse the blades and actually swim in reverse. I'm posting the Aqueon brochure, so everyone can see it.

I'm also re-posting my Hammerhead Unit disclosure, so it will be on this page of the thread. I'd appreciate any comments on it. Realize that some of the gain in streamlining is simply by putting your arms forward. This lengthens the diver's presentation to the water, and lessens the cross-sectional area presented to the water. But the Hammerhead Unit also provides additional propulsion by use of the blades. Because they can be independently twisted, you get the effect of forward wings for turning and making banks, etc.

The last part discusses the use of this device for handicapped divers. I have noted that handicapped divers underwater do not swim well. A paraplegic diver using this Hammerhead Unit would be able to use it as sole propulsion, and the motion would actually act on his/her fins too, providing some modest propulsion without muscular effort by that diver from the waist down. Finally, for a double amputee, combining the Hammerhead Unit with the Para-Sea BC harness, there is an attachment point for fins, or REVAN's monofin to be used by these divers.

SeaRat

 

[AlexL]

I think some really good videos with side by side comparisons of just how much more efficient your system is over conventional gear would be a great starting point. Maybe something like a scuba drag race filmed from the side to give people anvisual of just how much faster anscuba diver is able to be? Seeing people in a pool alone doesn't give any scope.

i think open water swimming side by side still retains too many variables. leg power, weight, cross section, stamina, energy levels, rig configuration, etc etc.

there's two sides to the problem. one being drag/resistance, and the other is propulsive efficiency.

IMO, the only proper way to experimentally test drag/resistance is to drop down on an anchor line with a steady current, and tie off using some sort of a load cell. bonus points if you have access to one of those infinity circulating pools where you can control the environment more precisely. then record average loading over time for whatever gear configurations you wish to try out while remaining in trim without kicking. with or without BC. BP/W vs BCD. with or without nose/tail cones. drysuit vs wetsuit vs skin vs bare. with or without the tank even attached (monkey diving). etc etc. lowest loading == lowest water resistance.

lowering drag resistance is an easy sell; less drag = less effort = lower SAC = longer air supply limited bottom time.

propulsive efficiency is a completely different beast to test empirically. if you can constrain the water resistance, kick/glide tempo, and kick force (via SAC/time), then average multiple runs over a known distance, you might get something close to useful info. faster/farther travel for the same kick tempo / kick force / SAC == more efficient.

fun part is that efficiency does not remain correlated vs kick force and kick tempo. hate to use car analogies, but its sort of like an engine's torque curve, there's a sweet spot where things are at peak efficiency, and elsewhere, its less efficient. some engines, like divers, like fins, prefer to dig in and pull hard against a big load, while others like to rev high against a light load. even with such different personality, they both could theoretically result in the same MPG/eff% numbers for one pace, while having wildly different MPG/eff% for a different pace. so there is a need to break things down into components and test each component / variable independently: fast vs slow kicking, hard vs easy exertion, long vs short stroke.

until someone comes forward with a properly controlled, repeatable, and reproducible experiment, this is all hand waving and hearsay.

 

[John C. Ratliff]

AlexL,

I think I have done something close to what you are requesting. Look at the Excel Worksheet, "Fin trails 3-12 & 27-2010 and tell me what you think. The bottom three entries are with my Hammerhead Unit (Forward Unit).

Under the tab, "Fin Trails 3-13-2010, the second set of numbers are with the Hammerhead Unit.

SeaRat

 

[REVAN]

@AlexL - Efficiency is very hard to measure, to the point where it is nearly impossible to get solid numbers without some elements of hand waving involved. Drag is less difficult if you treat the diver as a solid body object. The problem is that, unless they are being pulled by a DPV, they are not that at all. A diver must move his or her body to generate thrust, so the real drag is different from the solid body drag. It can get very complicated.

However, if you just focus on achieved swimming speed, you can get a good read on what is better or worse between two configurations. Add in SAC rate measurements and the information gets quite a bit better, but only if you do a really good job measuring the SAC. Variations in depth can make for very erroneous results, especially if you are shallow like you would be in a pool. Without the pool, the distances are unreliable unless you do a good job laying out a surveyed test track. The Tahoe Benchmark test track would be the ideal place to do the tests to get good data, but traveling there and doing it is no small or inexpensive operation. As you can see, properly testing the equipment can easily become a much larger job than is building the equipment.

In the end, I just decided to go to Hawaii where I can stay with friends and shoot some nice videos with the dolphins. It's certainly more fun than doing hardcore testing. I figured that if I show people that I can swim alongside the dolphins, that will make as good of an impression as any testing.

 

[AlexL]

I think I have done something close to what you are requesting.

getting closer for sure! course seems a bit short to separate the signal from the noise.

@AlexL - Efficiency is very hard to measure, to the point where it is nearly impossible to get solid numbers without some elements of hand waving involved. Drag is less difficult if you treat the diver as a solid body object. The problem is that, unless they are being pulled by a DPV, they are not that at all. A diver must move his or her body to generate thrust, so the real drag is different from the solid body drag. It can get very complicated.

this is very correct. my prior post should have specified this as `static` drag, rather then `dynamic` drag. i think its a case of 'learning to walk before running', if you reduce static drag, your dynamic drag will also be reduced. they may not correlate directly (untested assumption!), but they are somewhat related. in the end it really does come down to distance traveled over time vs RMV/SAC.

However, if you just focus on achieved swimming speed, you can get a good read on what is better or worse between two configurations. Add in SAC rate measurements and the information gets quite a bit better, but only if you do a really good job measuring the SAC. Variations in depth can make for very erroneous results, especially if you are shallow like you would be in a pool.

that’s where experimental controls come into play. might not all be able to use the same track, but if everyone agrees that the conditions of the test be held consistent, ie: tests runs are while following a V ft/m series of line strung at W FSW/MSW/FFW/MFW, with a water temp of X f/c +- X2 f/c using exposure protection Y mm with Z minutes immersed before the trial, resulted in A SAC, B kick cycle, and C velocity, then we can start talking about consistent data rather then abstract ideas.

granted, this only addresses the 'hard' data. personal preference still will weigh heavy on actual application.

 

[John C. Ratliff]

that’s where experimental controls come into play. might not all be able to use the same track, but if everyone agrees that the conditions of the test be held consistent, ie: tests runs are while following a V ft/m series of line strung at W FSW/MSW/FFW/MFW, with a water temp of X f/c +- X2 f/c using exposure protection Y mm with Z minutes immersed before the trial, resulted in A SAC, B kick cycle, and C velocity, then we can start talking about consistent data rather then abstract ideas.

granted, this only addresses the 'hard' data. personal preference still will weigh heavy on actual application.

You're talking about a Ph.D.-level physiology study. I participated in one of those years ago (1971) with the University of Oregon. I don't think either REVAN or myself is likely to get into that, although it would be fun. However, it would also be very, very time-consuming.

There is room for experience-based evidence, and I have presented quite a lot. Concerning the length of the swims above, 50 yards or 100 yards per fin or swimming stroke is about all this then 64 year-old could do. Those were maximal swims each time, so that is about what I can do. Now, at age 70, I hesitate to do more.

SeaRat

 

[REVAN]

My camera rig is not much different from your Hammerhead unit, @John C. Ratliff . It does not twist in the middle like your setup, but that is not a feature that I miss. I really don't think it is necessary to have that. I'm just using one of my monofin blades that I put some camera mounts on to hold cameras out to the side where I can get a good perspective angle for the camera. The foil helps to stabilize the camera to keep the shakiness down. I think it makes for some nice video shots.

 

[John C. Ratliff]

REVAN,

From earlier conversations (not this thread), I did not think you'd think much of the Hammerhead Unit. But basically, it is putting the propulsion blades, with more maneuverability, at the front of the diver instead of at the rear. On the rear the diver still has either his fins or a monofin. The Hammerhead Unit acts for both propulsion and stabilizing the dolphin kick. The loggerhead turtle, according to you, can do 5 knots using that same stroke.

I'm not sure whether you read the Aqueon brochure I posted above, but Mr. Gongwer documented a 1500 yard compass swim by divers (most probably U.S. Navy divers) using twin 90 cu. ft. tanks at 44 minutes and 30 seconds. If you do the math, that comes out to 2022.5 yards per hour, or 1.15 mi/hr. Using the Aqueon, they accomplished the same swim in 24 minutes, for a speed of 2.1 mi/hr using twin 90s (and probably an Aquamaster regulator). I am using the exact same blades off my Aqueon, but in a much more efficient manner, being controlled by my hands, not a spring. Why wouldn't they provide propulsion?

The use of fins on a camera is not new at all. Below there is a photo* from the 1950s of a movie camera stabilized by both horizontal and a vertical stabilizer. But that's to keep the camera steady, and not to provide propulsion.

In a similar fashion, I participated in a search for a downed helicopter off a Navy boat using a plane board (two divers in the water, each with a plane board), and being pulled by the boat. We had handles so we could dive the plane, or twist it and go around coral heads (we were diving off a small Ryukyu Island near Okinawa). At one point, my fellow PJ Billy R. Smith came up over a coral head, and the next thing we knew in the boat he was coming hand-over-hand up the line to get to the boat. He had come over that coral head and just about bumped a 8 foot shark in the snout. When he got into the boat, he said, "I don't like it. It's like we're trolling for sharks, and I'm the bait!" We stopped the search.

SeaRat

*Bronson-Howard, George, Handbook for Skin Divers, An ARCO How-To Book, ARCO Publishing Company, Inc., 480 Lexington Ave., New York 17, N.Y., no copyright or copyright date shown.

 

[lowviz]

John,

Just found this thread. Read it front to finish with great interest. Everybody thinks that great ideas come from big corporations. Not usually the case, big corporations BUY great ideas and make them theirs. If it wasn't for DOS you wouldn't get this post. DOS is IBM, no? NO!

Tim Paterson - Wikipedia, the free encyclopedia

Innovation is the anathema of groupthink. Ignore it. Keep the faith, persevere.

Kind regards.